Article made from powdered mixes and its manufacture



P 16, 1940- J. A. BOYER 2,197,655

ARTICLE MADE FROM POWDERED MIXES AND ITS MANUFACTURE I Filed July 28, 1936 1e4sc.

B o LIQUID.

LIQUID L Q PLUS SOL-ID. 800 c soup 0 (souo SOLUT Tm MELTE;

NALB +AL %SN 10 7 20 some.

nn rmunnnu INVENTOR.

JOHN A. aqverz ATTORNEY.

Patented Apr. 16, 1940 fum'rso STATES PATENT OFFICE Delaware Application 28, a

This invention relates to articles or compositions formed by the consolidation of powdered materials, and to their manufacture. I The in:

vention relates particularlyt'o the formingof articles' from powdered metals andto'themetal bondingof abrasives, but is also applicable to other types of materials. "One of the objects of theinvention is to facilitate the consolidation or diffusion of the particles of metal powder into a coherent mass without complete fusion'of the. powder, Another object is to provide an improved means for the bonding of, abrasive or other.non-metallic particles.

In the sintering of metal powders as ordinarily 5 carried out,'coh'erence of the particles to form a metallic body is accomplishedby difiusion of the atoms of metal across the surface boundaries of the particles while the metal is retained in the solid state. This difiusion requires intimate m contact between the particles, and for .this reason, very high pressures, such as are obtained in large hydraulic presses, are used. Even with high pressures, dlfliculties are often encountered in securing satisfactory coalescence of the particles 85 of powder.

- In the process which Iemploy, I form a mix of powdered metaIswhich becomes plastic on heating, as a result of the softening or melting 'of' one or more of the ingredients present. I have 30 found that diffusion takes place much more readily throughout the mass when a small quantity of liquid metal is present, then when themetals as powders are merely held in mechanical contact in the solidstate. By employing certain 35 types of mixes, as 'will be hereinafter described, it is possible to obtain a high degree of plasticity without the material becoming fluid, and in certain instances the liquid diffuses into the solid metal and the entire massre-solidifies at a higher 4) temperature. The melting of a portion ofv the material at a relatively low. temperature, followed by diffusion and resolidification at ahigher temperature, when combined with consolidation under pressure during the heating process, pro- 45 duces adense alloy material characterized by a high de'greeofstrength. Homogeneous metallic solid solutions'can be readily prepared by this method,"u sing the separate powdered components. v a

50 The nature of the present invention will be -more clearly understood from a consideration of the accompanying drawing.

In the drawing:

Figure 1 shows an equilibrium diagram of a 55 type of alloy which is plastic over a wide range o ftemperatures'without becoming fiuid, the speclfic example being the alloy system of aluminum andnickel.

F igure 2, shows; a portion of thelequilibrium diagram of, the copper-tinsyste'm, in which a solid solution is formed having an incipient melting point considerably higher than one of the components; I

, Figure 3 illustrates diagrammatically the meth- 0d of 'sinteringa thin circular article such as an 10 abrasive wheel under pressure:

Figure 4 illustrates a method of making an article such as metal bonded abrasive wheel, in which the heating current is passed directly through the mix and pressure applied during the 5 curing process; v

Figure 5 illustrates a method of forming a cylindrical article under pressure in a tube furnace;

Figure 6 shows a type of abrasive wheel which can be made by the process herein described. 20

Considering the drawing in detail, Figure 1 is a typical temperature-composition diagram of a number of alloy systems in which the temperature of incipient melting and the temperature of complete melting are widely divergent. In the 26 alloys of aluminum with nickel, cobalt and iron,

this property is very pronounced, and I have found that these alloys are plastic or pasty over a widerange of temperatures and compositions. The alloys have a number of physical properties, 30 as for example, stiifness in thin sections, a high degree of hardness, and the ability to chip under impact without being fragile, whichmake them suitable for many shaped metallic articles, and particularly for metal bonded abrasives.

The properties of alloys of this type under heat and pressure may be illustrated by considering the aluminum-nickel alloy series, with-particular reference to an alloy containing approximately per cent nickel. As shown in Figure 1, the temperature of incipient melting, indicated by the line A, remains constant for all alloys upto approximately 42 per cent nickel. The temperature of complete melting, however, rises rapidly, as is shown by the curve l2. In an alloy close to 45 the compound composition, as for example, that indicated by the line CD, most of the aluminum is combined in the form of the compound NiAh, but at the same time, the alloy has an incipient melting, point of. approximately 620 C. Upon as heating the-alloy to temperatures above the incipient melting point, sufficient melting takes place to render the material plastic, although the bulk of the alloy is unmelted. The plasticity of the material can thus be varied over wide limits without causing the material to become fluid. With lower nickel content, as for example, about 20 per cent nickel, the same,degree of plasticity can be obtained at temperatures immediately above the incipient melting point as is produced with the per cent alloy at somewhat higher temperatures. The powdered alloy can be readily molded to shape while plastic without the necessity of applying extremely high pressures.

Alloys, of aluminum with cobalt and iron which contain up to per cent cobalt or up to 30 per cent iron possess similar properties, and can be consolidated from powders in the same manner as the aluminum nickel alloys.

In making sintered compositions from powdered alloys where intermetallic compounds are formed, it is desirable to previously alloy the material and then reduce it to a powder. In the case of the aluminum alloys, this preliminary alloying greatly reduces the amount of liquid which would be present if compositions high in free aluminum were used, and also decreases the harmful effect of the chemical reactivity of aluminum in ab sorbing oxygen, nitrogen and carbon.

In an alloy series in which no compound is formed, but in which the temperatures of incipient and final melting are widely separated,

the pure metal powders can be used, and the sintering temperature regulated so that the mass contains a small proportion of liquid. Alloys 01. copper with small percentages of bismuth, for example, can be consolidated by this method. Intermetallic compounds can also be mixed with powdered metals so as to form a plastic mass on heating. Mixtures of this type can be readily formed to shape by applying pressure either during the plastic stage or throughout the heating process.

When metallic objects of high strength and ductility are required, solid solution alloys can be formed under pressure from a mixture of their components. If one of these components melts at a temperature below the incipient melting point of the solid solution formed, a portion of the mix will become fluid on heating, thus rendering it plastic, but upon heating the mix to a higher temperature, the liquid will diffuse into theunmelted material and the entire mass will solidify to-form a homogeneous solid solution alloy. Pressure can be applied during the partially liquid stage, or if desired, during the entire time of heating.

A composition of this type is illustrated in Figure 2, where the alloy is a solid solution of copper and tin. If a mixture of powdered copper and tin containing, for example, 10 per cent tin is heated to a temperature above 232 C. (the melting point of tin), the tin contained in the mix will melt, but as it is only a minor proportion 01' the mixture, the mass will become plastic" rather than fluid. Upon raising the temperature to a point where diffusion of the tin into the copper is rapid, the tin will disappear as a separate constituent, and the mass will become solid, owing to the formation of the solid solution alloy. The partial liquefication of the mix before a1- loying not only facilitates diffusion, but also makes the powdered material more readily delormable under pressure. For this reason, it is desirable to apply pressure during the heating process. The pressures required, however, are considerably less than those usually employed in the forming of sintered articles from metal powders.

Examples of other alloys of this type are the solid solution alloys of copper with aluminum and zinc, and the solid solution alloys of nickel containing copper.

Even in cases where partial or incipient melting does not take place, I have found that there is a general relationship between the rate of diffusion or degree of coalescence of the metal powder at a given temperature and pressure and the presence of a low melting constituent or eutectic in the final alloy. For example, if two metals are employed which form a eutectic melting at a lower temperature than either component metal, alloys made from the original component powders can be readily produced by diffusion at temperatures just below the melting point of the eutectic, evenwhen this temperature is considerably belowthe melting point of either powder making up the mix. As a specific illustration, copper and silver form a eutectic which melts at 778 C. and contains 72 per cent silver. Thus, if mixtures are formed from copper and silver powders and the mass sintered at temperatures slightly belowthe eutectic temperature, coalescence can be. readily efiected. The closer the eutectic composition is approached, the more readily can the particles of powder be consolidated into a dense metallic mass at temperatures slightly below the eutectic temperature. As in other previous examples, the mix becomes plastic,

as the eutectic temperature is approached, and the application of pressure during heating greatly facilitates coalescence.

In carrying out the sintering process, it is desirable to coat the metal particles with a solution of a fiuxing agent, as described in my copending application Serial No. 93,037, filed of even date herewith. This is particularly true in the case of copper and copper base solid solution alloys, and also the nickel base alloys. The flux for these alloys can consist of a solution of borax and boric acid in the proportion of two parts of borax to one part of boric acid, or a solution of borax and an acid fluoride such as potassium acid fluoride. In the case of the aluminum alloys where the material at the final sintering temperature contains a certain proportion of liquid, satisfactory coalescence can usually be obtained without the use of a flux, butv a dilute solution of aluminum welding flux can be used to moisten the powder if desired.

The compositions of the type above described are well adapted for the bonding of abrasives, and impart to the abrasive article certain characteristics which cannot be obtained with other types of bond. For example, the solid solution alloys are tough and resilient, and when abrasive articles in which these alloys are the bonding agents are made by the process herein described, the wheels will out very hard materials rapidly, and at the same time the bond is so tough that the wheel loss is small or negligible compared with the usual abrasive wheel in which the bond is a ceramic or an organic material. These tough resilient bonds are especially adapted for abrasive wheels containing diamonds, for the diamond will retain its cutting qualities much longer than other abrasives, and with the usual diamond wheel the abrasive particles are separated from the wheel before their full cutting power has been utilized. The characteristics of the bond can also be varied over a much Wider range than is possible with the usual abrasive bonds. For

example, the solid solution alloys are very tough and resilient, and thin wheels sintered from these materials can even be made flexible if desired,

whereas'the alloys approaching the composition of an intermetallic compound are very rigid and .hard, and in many instances will break before bending. By controlling the composition'of al- 'loys containing intermetalli'c compounds, it is possible also to produce a bond'which will break down under impact, and which at the same time will be very hard and rigid. This breakdown during the use of the wheel is important in.main- .taining a freecutting surface, particularly in connection with abrasives softer than the diamond. In cutting certain materials with a metal bonded Wheel in which the abrasive is silicon carbide or boron -carbide, the wheel will often glaze over if .a ductile resilient metal or alloy is 'used'as the bond, but if a hard alloy is used, and particularly an alloy which will break under impact, glazing .is prevented, and a wheel can be produced which is practically self-dressing.

In'the case of metal bonded diamond wheels, I have found it to advantage to include in the mixture a certain proportion of a softer abrasive such as silicon carbide, boron carbide or fused alumina. This softer abrasive is preferably somewhat finer in grit size than the diamonds, and when it is distributed through the matrix, it stiffens the metal and makes it very resistant to wear'or abrasion.*'I'hus, even in cases when the softer abrasive does no cutting whatever, it greatly reduces the wheel loss, which is ordinarily due to undercutting or tearing out of the metal matrix surrounding the diamonds. The addition of materials such as silicon carbide to the mix makes possible the use of a comparatively small percentage of diamonds of fairly coarse grit to 'do the cutting, with-practicallyno wearingor tearingout of the surrounding matrix. The action of the softer abrasive in making the matrix resistant to wear is of special importance in the use of cut off wheels for cutting glass, silicon carbide and other hard materials which in themselves have abrasive characteristics.

During the cutting operation a considerable portion of the wheel is buried in the cut, and the detritus formed in the cut, :being finely divided, has a lapping effect upon the metal in which the diamonds are embedded. This lapping or wearing away is prevented by the presence of the abrasive distributed throughout the matrix between the particles of diamonds.

The method of carrying out the invention, as illustrated in the accompanying drawing, is directed for the most part to the manufacture of metal bonded abrasive wheels, although it will be realized that practicallyany form of shaped article, composed entirely of metal or consisting of non-metallic particles embedded in or bonded by metal, can be produced by the methods indicated. Specific methods by which the sintering operation can be carried out are illustrated in Figures 3 to 5 inclusive. Referring to these figures in detail,"Figure 3 shows a furnace with a wire heating element 2 embedded in the wall of the furnace chamber. A hand press supported by the steel frame 3 is placed over the furnace so as to engage with the plunger 4. The screw jackfi, when turned, applies pressure to the plunger 4, and hence to the plunger 6 of the mold. The mold is composed of an outer shell I, which can be made of metal, and two plungers B .and 8, which are preferably made of carbon or Acheson graphite. These two plungers are centrally bored to receive an insert or plug 9, which first positioned around thebottom plunger 8 so as to form a container, and the insert 9 is also inserted in the hole in the bottom plunger. The mix isthen introduced into the mold and the top plunger inserted. After the mold is assembled, pressure can be applied during the heating operation by means of the screw handle 5.

Instead of applying the pressure continuously as indicated in Figure 3, the pressure can be applied by a sudden blow or a series of impacts, as in a forging or swaging operation. Such a procedure assists in eliminating the air film surrounding the unmelted metal particles or the non-metallic particles. contained in the mix, and thus facilitates coalescence of the .metal andadhesion of the metal to the non-metallic particles. Jolting the mix during application of pressure willalso produce a similar effect.

Figure 4 illustrates a carbon electrode furnace in which the mold is placed between two large carbon electrodes l2 and pressure applied by means of the hand screw 13. The current is passed directly through the plungers l4 and the mix I5 so as to heat the material to the desired temperature. a

Figure 5 illustrates a tube furnace in which a carbon tube I! functions as the resistor, and is positioned between two carbon electrodes [8 and I9. Electrode I8 is hollow so as to admit the plunger '20 which transmits pressure to the mold plungers. The mold consists of an outer ring 2| and two plungers 22 and 23, which are bored to receive the plug 24. The mix 25 is placed around the plug so as to form acircular body with a hole through the center.

Figure 6 shows a type of abrasive wheel made by my process,'which has been'found satisfactory for the cutting of glass, bonded silicon carbide,

refractory tile, and other extremely hard materials. The outer rim Z1 is composed of diamonds which are embedded in .sintered metal. Silicon carbideyboron carbide or other abrasive materials can be mixed with the diamonds in this outer rim. The inner portion 28 of the wheel can be composed entirely of metal or can'be composed of a mixture of metal and an abrasive filler such as silicon carbide.

As a specific example of one method which can be used in making the wheel, the following procedure is given:

A mixture containing 10% diamonds of any desired grit size (as for example from 50 to 150 grid), 10% silicon carbide, 72% copper powder and 8% tin powder is moistened with an aqueous solution of borax and potassium acid fluoride. (This solution may also contain potassium carbonate and boric oxide.) Excess moisture is removed from the mixture, and'after the lumps proximately 150 grit), 72% copper powder and 8% tin powder is made. This mixture is also moistened with the flux and, after drying or removing at least most of the excess moisture, is introduced into the mold. The mold is then assembled as shown in Figures 3, 4 or 5 and the mixture subjected to pressure and at the same time heated to a temperature of approximately 750 C.

--'coated paper or cloth and'the disc to which the abrasive is to be joined and the-sintering operavtion carried out as above described. I

: particlesand a metal powder as described inthis In addition to the metal bonding oi abrasives, the process herein described is applicable to the charging oi the surface or a metal wheel or grinding disc such as is used for the grinding or glass. For this purpose a mixture of diamonds or other abrasive and metal powder can be spread in a thin layer over the bottom suriace oi the mold. and the metal disc used as a plunger or inserted between the mold plunger and the layer of abrasive and metal powder. If a single layer of abrasive is desired, the abrasive grains can be coated on a paper or cloth which is covered with adhesive, the metal powder inserted between the I havefound that sintered mixtures of abrasive application form excellent[bearing surfacesQsince the hardparticles in thematrixar'e resistant to wear andthe, metal in which they are embedded is suilicientlyv ductile to withstand shock: or impact. Abrasive'materials such as-sili'con carbide,

- boron. carbide or fusedzilumina are many times harder than the interme'tallic compoundsv found inmost bearing metals, .so that the-bearing will last almost indefinitely'without appreciable. war. Fine silicon-carbide .orl fused alumina particles embedded-in a ductile matrix suchas copper. or] air r s st n Pr pe i bronze have excellent we .when usedj for this purpose. V V

While the invention is primarily intended for the production of shapediarticles'fit*can also' be numv-n ickel alloys-will make evident- -the n ean- I H aluminum (in nine; form f'of falu inm used for forming metal bonded abrasive aggrev gates. For example, fine g rit diamonds or other V abrasive can 'be bonded witnmetal by the process fdesc'ribed; andth'e'bon'ded mass broken intoparticles considerably-coarser thantheoriginal grit size of the abrasive. a By the term "-ing'redient-in-the appended claims I mean any component orconstituent of the alloy in-theform in which it is present in "the powdered mix.

ILalso include eutectics within the scope of this term,isince-a. eutectichas a constant 'composition,-melts at a constant tem perature, and'behaves asa singlegsubstance upon heatingi-wn A-fewexamples in .connection -w mansilng, of theterm: n redierit.{? alloy con if .powdered,.

umv nickel veutectlccontaining about ten'per 'centl'of nickel),

. as will be evident from a considerationof'flifigure 1 o; the drawing. a The powderedmaterial,

feven if previously alloyed, would thus contain an ingredient having a melting point below the temperature of complete fusion of the alloy; If

' a composition corresponding to the' pure 'com pound NiAlwere introduced into the"m'ix"' in theform of the'componen't powders, the mixtime would also contain a low melting ingredient,

' namely, aluminum. However, an all'oy of this cornp'osition', if powdered; would-not contain an ingredient having a lower melting point than in'the mix in any form which would melt at a low temperature. 7

The term "component" is used lnits usual phase rule interpretation, in that it represents the elements or compounds from which the alloy system or equilibrium diagram is built up, regardless of their state of combination in the particular mixture or alloy in question. the aluminum-nickel system the components usually chosen are aluminum and nickel, and these elementsremain the'components even .in alloy compositions where neither element is presentln the'freestate' l r A constituent may, be defined as a phase which can .be separately identified under the microscope. Thus, inasolidsolution. of tin in copper, there are two components (namely. copper and tin) but only one constituent, which is the so id solution;

j. "Having thus described my invent'ion, I claim:'

1."'I'he process of forming an abrasive article inwhich the abrasive is bonded by-a metal: alloy consisting essentially of a solid solution, which comprises forming a mix containing abrasive grain and at least two components of the said solidsolution in finely divided form, one of said components being present in minor proportion and havinga melting point substantially lower than the temperatureofcomplete melting of the ,thealloy of the bond is predominantly the ductile alpha solid' solution of copper and tin and the metal components t the alloy in the mix are ppe and, tin. I

4. 'Iheprocess according to claim 1 in which ,th. ano'yfof the bond, is predominantly a solid solution of aluminum in copper andithe metal components of the alloy in the mix are aluminum andifcop'per 5. The process according to claim 1 in which the'alloy of the bond is predominantly asolid solution of zinc incopper and the metal components of the alloy in the mix are zinc and copper."

6. The process accordingto claim 1 in which the alloy of the bond is predominantly a solid solution of 'tin in'copper and the metal components of the alloy in, the mix are tin and copper. i

- JOHN A. BOYER.

Thus in I 

